1. Field of the Invention
The present invention relates to a rotary electric machine such as a motor or a generator.
2. Description of the Related Art
JP-U-60-38063 discloses a DC motor as a rotary electric machine.
This rotary electric machine includes a frame having a concave bearing box at the rear center thereof, a stator fixed to the frame and a rotor that is disposed inside the frame and rotatably supported thereby. A bearing is fitted to the inside of the bearing box to support the rear portion of the rotor shaft. A bearing cover, which is called as a dust-proof cap, is fitted to the bearing box to cover the rear portion of the bearing.
From the drawings, it is presumed that this bearing cover together with rear frame is made of metal and, provably, steel. In other words, the bearing cover is a unitary member having a disk-shaped bottom and a short hollow cylindrical portion that is mechanically extended from the outer periphery of the bottom. The bearing cover is pressed into the back of the bearing box to close the open end of the bearing box.
However, the above metal bearing cover is force-fitted to the bearing box of the rear frame. Therefore, a permissible dimensional deviation of the outside diameter of the bearing cover is required to be very small, resulting in a high production cost.
Further, because of the metal-to-metal force fitting, the contact surfaces thereof may be easily scratched, thereby, to allow water into the inside bearing cover.
It is necessary to remove the bearing cover whenever the bearing is replaced. Because the bearing cover is force-fitted into the bearing box, it is not easy and takes time to remove the bearing cover. Moreover, the end frame may be damaged during the difficult removing work of the bearing cover. Therefore, such a bearing cover once removed is not so easy to use again. Even if it can be used again, the working cost may be too high.
A main object of the invention is to provide a rotary electric machine having a waterproof and readily removable bearing cover that can be used again.
According to a feature of the invention, a bearing cover that is fitted to a bearing box is a cup-shaped unitary member made of rubber. The bearing cover has a hollow cylindrical portion, a plurality of ring-shaped projections on the periphery thereof and a bottom for sealing or closing the open end of the hollow cylindrical portion.
The bearing cover is inserted into the back of the bearing box after the bearing. The bearing cover is a mold of an elastic material that can be fitted or inserted into the bearing box by hand. The bearing cover can be easily removed from the bearing cover by hand, or a screwdriver if necessary. If a knob is formed on the bearing cover, it can be removed more easily.
Because the material of the bearing cover is rubber or soft resin, the permissible dimensional deviation of the outside diameter of the bearing cover can be made rather large, thereby reducing the production cost. Even a small gap may not form between the bearing cover and the bearing box.
Because a plurality of elastic ring-shaped projections contacts the inner periphery of the bearing box, the bearing box is completely waterproofed.
When the bearing cover is removed from the bearing box to replace the bearing, it is easy to form gaps between the light and elastic ring-shaped projections and the inner periphery of the bearing box. Therefore, a screw driver can be inserted into one of the gaps easily, and the bearing cover can be easily removed in a very short time. As a result, no scratch may form on the bearing box, and the bearing cover once removed can be used again.
In the meantime, xe2x80x9cbackwardxe2x80x9d means an axial direction of the rotary electric machine in that the bearing box opens. It is opposite to the direction in that the rotor shaft extends xe2x80x9cforwardxe2x80x9d from the frame.
According to another feature of the invention, a plurality of ring-shaped projections inclines backward. When the bearing cover is fitted to the bearing box, the outer periphery of the plurality of the ring-shaped projections easily contracts. Therefore, a small pressure is only necessary to fit the bearing cover into the bearing box. On the other hand, the outer periphery of the ring-shaped projections expands when the bearing cover is pulled in the removing direction or backward. Therefore, the bearing cover is not easy to remove.
If the bearing box with the bearing cover being fitted therein is vibrated, the inclined ring-shaped projections urge the bearing cover forward (deeper in the bearing box). Therefore, the bearing cover is prevented from dropping out of the bearing box. If the internal pressure of the rotary electric machine increases to push the bearing cover backward, the ring-shaped projections retain the bearing cover securely.
According to another feature of the invention, the bottom of the bearing box is thinner than the peripheral wall of the hollow cylindrical portion. In addition, because the bearing box is made of an elastic material, the bottom expands as the internal pressure of the bearing box increases so as to absorb the increased internal pressure.
According to another feature of the invention, the bearing cover has a knob that projects backward. Therefore, it is possible to easily remove the bearing cover from the bearing box with the knob being pulled by hand or a tool. Accordingly, not only the bearing cover is easy to remove but also the bearing cover and the bearing box are protected from damages.